I wouldn’t call it coding. It’s more about writing configurations. You have to provide a list of packages you need and some configuration for them like configuring default desktop environment. I recommend searching for dotfiles repos with configuration.nix on github to get an idea.

Community is growing fast in recent years and more and more companies are using it. I know a big real estate company is using it but you won’t hear about nixos when buying a property from them.

It’s same like unit tests or static typing. It’s extra work and some don’t think the benefits are worth it. On top of that the learning curve for nix is steep.